WA Sales Tax Lookup

Reliable, self-hosted REST API for Washington State sales tax rates.
Built for ecommerce, payment processing, and tax compliance.

Try the API View on GitHub

Why WA Sales Tax Lookup?

WA Sales Tax Lookup provides a modern, reliable alternative to Washington State's tax lookup infrastructure. Whether you're building an ecommerce platform, payment processor, or tax compliance system, this API gives you complete control and independence.

  • ✓ Address-based tax rate lookup with geocoding
  • ✓ Self-hosted or microservice deployment
  • ✓ Quarterly automatic data updates from the State
  • ✓ High-performance .NET 10 Minimal API
  • ✓ Multiple response formats: JSON, XML, plain text
  • ✓ Interactive Scalar API documentation
  • ✓ Backward compatible with State API
  • ✓ AGPL v3 Open Source licensed
Zero State Infrastructure Dependency: Once deployed, your application is independent from Washington State's IT infrastructure. The tax data is cached locally and automatically updated quarterly.

Built for Performance & Reliability

Based on the official Washington State Department of Revenue API, but with a modern JSON response option. This project implements best practices for address normalization, including smart abbreviation of street names and address elements—improving geocoding accuracy when exact matches aren't found.

.NET 10 ASP.NET Minimal API REST API Scalar Docs ESRI Geocoding

Easy Integration

Query by address and ZIP code, with optional city parameter. Get back precise tax rates with state, local, and RTA (Regional Transit Authority) rates. Perfect for checkout flows, tax calculation, and compliance reporting.

Assembled on the shores of Lake Union by Thomas Ryan. Licensed under AGPLv3.